1. Field of the Invention
The present invention relates to pulverulent adhesive compositions, to processes for their preparation and to their use in formulations for the adhesive bonding of porous and semiporous substrates.
2. Description of Related Art
In order to avoid solvent wastes and solvent emissions, aqueous dispersions are increasingly being employed, in accordance with TRGS 610/GISCODE, as binders for producing pollutant-free adhesives. Suitable aqueous dispersions usually include, in addition to a synthetic, free-radically polymerized polymer, also tackifying resins, known as tackifiers. Such aqueous dispersions are described, for example, in U.S. Pat. No. 4,654,388, DE-A 23 01 497, EP-A 0 221 461, EP-A 0 315 070, EP-A 0 490 191 and EP-A 0 620 243.
These resins are generally rosins or esters thereof, and also hydrocarbon resins, which can if desired be esterified or otherwise modified. Aqueous resin dispersions with resin contents of between 50 and 70% by weight are generally also employed as tackifiers. The tackifier resin is added, generally in the form of an organic solution or else as a resin melt, to an aqueous dispersion of the polymer, or is added to the dispersion in combination with a wetting agent, plasticizer or high-boiling component. When aqueous resin dispersions are used, all that is generally required is a simple combination with a polymer dispersion appropriate as a binder. Since aqueous products form a good nutrient substrate for microorganisms, they are generally treated with a preservative. Examples of preservatives employed include chloroacetamide, N-methylolchloroacetamide, 2-bromo-2-nitropropane-1,3-diol or isothiazolinones. EP-A 0 134 451 discloses dispersion powders which can be employed for preparing adhesives but which do not themselves possess sufficient tack.